Many products are sold in plastic bottles. Plastic bottles have cost and other advantages over their glass and metal counterparts. One disadvantage is it is relatively difficult to apply labels to them.
The use of pre-printed and pre-formed plastic sleeves as labels is gaining increasing acceptance as a preferred, if not the preferred, method of labeling such plastic bottles. A method and machine for labeling bottles with plastic label sleeves is described more fully in U.S. Pat. No. 4,620,888 issued Nov. 4, 1986 to William M. Easter et al. entitled "Labeling Apparatus". The disclosure of that patent is incorporated by reference.
Sleeve-type labels are typically made with polyethylene film. The film is first printed to provide the decoration and information desired. The film is then folded and a longitudinal seal is formed to convert the folded film into a tube. Transverse perforations are then formed to delineate the ends of the sleeves and the perforated tube is then coiled and shipped to a location where bottles are to be labeled.
One technique which has been used for forming bead seals in superimposed film layers in the manufacture of tubing utilizes so-called "hot knives". A hot knife is a metallic element which is heated to both sever and seal superposed film layers. While hot knives have long been used, they are not fully satisfactory for the manufacturing of sleeves because they are the limiting factor as to the speed with which sleeves can be manufactured.
As an expedient to improve the rate at which sleeves are manufactured, lap seals have been formed. With this technique, edge portions of superposed layers of film were heated with hot air to form a seal. When the sleeve was put over a bottle this seal formed a projection known as a "flag" which was objectionable from an appearance standpoint.
So called "flame sealing" of plastic film has been known for a number of years. For example, one technique used to make sample sleeves and bags is to place two layers of film between superposed precision plates with small edge portions of the film projecting from the plates. The projecting film is then heated with a propane torch to form a bead seal. This procedure has not been satisfactory for production techniques because it is slow.
There have been proposals for providing an in-line series of flame jets. Such proposals typically would utilize a tube as a manifold. The tube would have an axially aligned series of spaced holes drilled in it through which natural gas or propane was to be projected to provide an in-line set of flames. While there have been such proposals, so far as we are aware, they have not proved successful at least to provide quality seals at the high production rates desired for sleeve manufacture.